This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The inability of previous studies to trap and study a pre-triggered state of the GroEL-GroES complex is not surprising, given that wild-type GroEL populates this allosteric state only transiently (for about a hundred millisec), too short a time for most biochemical and biophysical manipulation. By contrast, our modified GroEL variant appears to undergo this transition at a considerably slower rate. We propose that a high-resolution structure of this new GroEL variant, exploiting the technical advances the NCMI has made in examining molecules like GroEL by cryo-EM, is likely to provide an unprecedented snap-shot of a critical allosteric state of the GroEL-GroES machine about which little is known.